A little Information About Angelman Sysndrome
For those unaware there are several types of Angelman Syndrome a neuro genetic condition.
Everyone has two copies of the UBE3A gene, one from their mother and one from their father. In the brain, due to a biological quirk called imprinting, we only use the UBE3A gene we inherit from our mother – the paternal copy is ‘switched off’.
Deletion form (also known as Del +ve):
The majority of individuals with Angelman Syndrome (approx. 70%) are missing the region of chromosome 15 containing the mother’s copy of UBE3A – it has been deleted in the AS individual. This happens solely in the affected child – the mother is unlikely to have a further child with AS and any siblings of the AS individual are unlikely to have children with AS. There is the possibility that the mothers 15th chromosome has an alternative arrangement called a translocation, which may have been part of the cause of a deletion, but this is incredibly rare although does happen.
Uni-Parental Disomy form (UPD)
In some cases (approx. 1%), a person with Angelman Syndrome has two copies of the “switched off” paternal UBE3A gene. In this case, all of the chromosome 15 is present, but neither UBE3A copy is “switched on”.
Some individuals (approx. 11%) have mutations (simple changes to the genetic code) in the maternal UBE3A gene that prevent it from being functional.
Sometimes (approx. 5% of AS individuals) there are changes in the UBE3A gene that cause the maternal copy to act as if it was the paternal copy. These are called imprinting defects.
In approximately 10% of cases diagnosed to date, the cause is unknown.
A very small number of AS individuals have a “mosaic” form of AS, whereby a small percentage of cells in the brain have a normal copy of the maternal UBE3A, but the majority have an inactive copy. Individuals with this type of AS tend to have a milder form of the disorder. This form of the syndrome is hereditary. There is a risk that a mother may have one or more children with AS and those children that don’t have AS may pass AS on to their children.